Add collision handling and snow behavior validation

[utilForever]

This revision includes:

• Add collision handling and snow behavior validation (Closes Add collision handling and snow behavior validation #164)
  • Include zero-gap collider contact
  • Add snow MPM collision handling
  • Expose snow MPM domain boundaries to Python
  • Validate snow MPM collision stability

Summary by CodeRabbit

• New Features

  • Added configurable closed-domain boundaries for snow simulations in 2D and 3D.
  • Exposed boundary configuration through the Python API.
  • Improved particle and grid handling at domain boundaries, colliders, and frictional surfaces.

• Bug Fixes

  • Improved collision handling for particles exactly touching collider surfaces.
  • More reliably prevents particle penetration and constrains positions and velocities.

• Tests

  • Added coverage for boundary settings, moving colliders, friction, exact-surface collisions, and simulation stability.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Configuration used: Organization UI

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Run ID: 0b4a6650-ff8a-48a7-a4eb-dfa8bee185f1

📥 Commits

Reviewing files that changed from the base of the PR and between 386806d and 4f6f332.

📒 Files selected for processing (1)

• Includes/Core/Solver/Particle/MPM/SnowMPMSolver-Impl.hpp

🚧 Files skipped from review as they are similar to previous changes (1)

• Includes/Core/Solver/Particle/MPM/SnowMPMSolver-Impl.hpp

📜 Recent review details

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📝 Walkthrough

Walkthrough

Snow MPM now supports configurable closed-domain boundaries, grid and particle constraints, inclusive collider contact detection, Python property access, and validation for walls, moving colliders, friction, exact contact, and finite simulation state.

Changes

Snow MPM constraints and validation

Layer / File(s)	Summary
Closed-domain boundary API Includes/Core/Solver/Particle/MPM/SnowMPMSolver.hpp, Includes/Core/Solver/Particle/MPM/SnowMPMSolver-Impl.hpp, Sources/API/Python/Solver/Particle/MPM/SnowMPMSolver.cpp, Tests/PythonTests/test_snow_mpm_solver.py	SnowMPMSolver stores a closedDomainBoundaryFlag initialized to DIRECTION_ALL. C++ and Python accessors expose the setting.
Time-step boundary and collider constraints Includes/Core/Solver/Particle/MPM/SnowMPMSolver.hpp, Includes/Core/Solver/Particle/MPM/SnowMPMSolver-Impl.hpp, Tests/UnitTests/SnowMPMSolverTests.cpp	The solver constrains grid velocities before deformation updates and projects particle positions and velocities after grid transfer. Tests cover 2D and 3D walls, moving colliders, friction, and open versus closed boundaries.
Inclusive contact and behavior validation Sources/Core/Geometry/Collider.cpp, Tests/UnitTests/RigidbodyCollider2Tests.cpp, Tests/UnitTests/RigidbodyCollider3Tests.cpp, Tests/ManualTests/SnowMPMSolverTests.cpp	Collider detection includes exact surface contact and exact radius distance. Tests cover zero-radius contact and finite frictional Snow MPM state.

Estimated code review effort: 4 (Complex) | ~45 minutes

Sequence Diagram(s)

sequenceDiagram
  participant SnowMPMSolver
  participant Grid
  participant Collider
  participant Particles
  SnowMPMSolver->>Grid: constrain grid velocities
  Grid->>Collider: resolve collider contact
  Collider-->>Grid: return corrected velocity
  Grid-->>Particles: transfer constrained motion
  SnowMPMSolver->>Particles: project positions and velocities

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Possibly related PRs

• utilForever/CubbyFlow#171 — Relates to SnowMPMSolver behavior built around the snow deformation state.
• utilForever/CubbyFlow#175 — Directly extends the SnowMPMSolver implementation, API bindings, and tests.

Poem

A rabbit checks the snowy grid,
Each wall holds fast as it was bid.
Colliders turn each closing glide,
Exact-touch tests stand beside.
The particles stay safely inside.

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Linked Issues check	⚠️ Warning	The changes cover collision handling, boundaries, penetration prevention, collider tests, and finite-state validation, but do not clearly verify hardening and yield-limit behavior required by issue #164.	Add focused tests for compression hardening and permanent deformation from tensile and compressive yield limits.
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the pull request’s collision-handling and snow-validation changes.
Out of Scope Changes check	✅ Passed	The collider comparison change, Snow MPM API updates, implementation changes, and tests directly support the linked issue objectives.

✨ Finishing Touches 💡 1

📝 Generate docstrings 💡

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch collision-handling

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[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

View in Codacy

🟢 Metrics 44 complexity · 6 duplication

Metric	Results
Complexity	44
Duplication	6

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[codecov]

Codecov Report

❌ Patch coverage is 98.03922% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 83.62%. Comparing base (cb2b1cf) to head (4f6f332).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #177      +/-   ##
==========================================
+ Coverage   83.57%   83.62%   +0.04%     
==========================================
  Files         418      418              
  Lines       23807    23855      +48     
==========================================
+ Hits        19897    19948      +51     
+ Misses       3910     3907       -3     

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
4 Accepted issues

Measures
0 Security Hotspots
45.1% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud